diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..9b1ee42
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,175 @@
+# Based on https://raw.githubusercontent.com/github/gitignore/main/Node.gitignore
+
+# Logs
+
+logs
+_.log
+npm-debug.log_
+yarn-debug.log*
+yarn-error.log*
+lerna-debug.log*
+.pnpm-debug.log*
+
+# Caches
+
+.cache
+
+# Diagnostic reports (https://nodejs.org/api/report.html)
+
+report.[0-9]_.[0-9]_.[0-9]_.[0-9]_.json
+
+# Runtime data
+
+pids
+_.pid
+_.seed
+*.pid.lock
+
+# Directory for instrumented libs generated by jscoverage/JSCover
+
+lib-cov
+
+# Coverage directory used by tools like istanbul
+
+coverage
+*.lcov
+
+# nyc test coverage
+
+.nyc_output
+
+# Grunt intermediate storage (https://gruntjs.com/creating-plugins#storing-task-files)
+
+.grunt
+
+# Bower dependency directory (https://bower.io/)
+
+bower_components
+
+# node-waf configuration
+
+.lock-wscript
+
+# Compiled binary addons (https://nodejs.org/api/addons.html)
+
+build/Release
+
+# Dependency directories
+
+node_modules/
+jspm_packages/
+
+# Snowpack dependency directory (https://snowpack.dev/)
+
+web_modules/
+
+# TypeScript cache
+
+*.tsbuildinfo
+
+# Optional npm cache directory
+
+.npm
+
+# Optional eslint cache
+
+.eslintcache
+
+# Optional stylelint cache
+
+.stylelintcache
+
+# Microbundle cache
+
+.rpt2_cache/
+.rts2_cache_cjs/
+.rts2_cache_es/
+.rts2_cache_umd/
+
+# Optional REPL history
+
+.node_repl_history
+
+# Output of 'npm pack'
+
+*.tgz
+
+# Yarn Integrity file
+
+.yarn-integrity
+
+# dotenv environment variable files
+
+.env
+.env.development.local
+.env.test.local
+.env.production.local
+.env.local
+
+# parcel-bundler cache (https://parceljs.org/)
+
+.parcel-cache
+
+# Next.js build output
+
+.next
+out
+
+# Nuxt.js build / generate output
+
+.nuxt
+dist
+
+# Gatsby files
+
+# Comment in the public line in if your project uses Gatsby and not Next.js
+
+# https://nextjs.org/blog/next-9-1#public-directory-support
+
+# public
+
+# vuepress build output
+
+.vuepress/dist
+
+# vuepress v2.x temp and cache directory
+
+.temp
+
+# Docusaurus cache and generated files
+
+.docusaurus
+
+# Serverless directories
+
+.serverless/
+
+# FuseBox cache
+
+.fusebox/
+
+# DynamoDB Local files
+
+.dynamodb/
+
+# TernJS port file
+
+.tern-port
+
+# Stores VSCode versions used for testing VSCode extensions
+
+.vscode-test
+
+# yarn v2
+
+.yarn/cache
+.yarn/unplugged
+.yarn/build-state.yml
+.yarn/install-state.gz
+.pnp.*
+
+# IntelliJ based IDEs
+.idea
+
+# Finder (MacOS) folder config
+.DS_Store
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..d132390
--- /dev/null
+++ b/README.md
@@ -0,0 +1,20 @@
+# bigint-quantile
+
+Easily calculate quantiles for large datasets.
+
+## Installation
+
+```bash
+$ npm install bigint-quantile
+```
+
+## Usage
+
+```ts
+import { calculateQuantile } from "bigint-quantile";
+
+const data: bigint[] = [1n, 2n, 3n, 4n, 5n, 6n, 7n, 8n, 9n, 10n];
+const quantile = 0.5;
+
+const result = calculateQuantile(data, quantile);
+```
diff --git a/biome.json b/biome.json
new file mode 100644
index 0000000..d9938df
--- /dev/null
+++ b/biome.json
@@ -0,0 +1,30 @@
+{
+	"$schema": "https://biomejs.dev/schemas/1.9.1/schema.json",
+	"vcs": {
+		"enabled": false,
+		"clientKind": "git",
+		"useIgnoreFile": false
+	},
+	"files": {
+		"ignoreUnknown": false,
+		"ignore": ["dist/**/*"]
+	},
+	"formatter": {
+		"enabled": true,
+		"indentStyle": "tab"
+	},
+	"organizeImports": {
+		"enabled": true
+	},
+	"linter": {
+		"enabled": true,
+		"rules": {
+			"recommended": true
+		}
+	},
+	"javascript": {
+		"formatter": {
+			"quoteStyle": "double"
+		}
+	}
+}
diff --git a/build.config.ts b/build.config.ts
new file mode 100644
index 0000000..bd3382b
--- /dev/null
+++ b/build.config.ts
@@ -0,0 +1,11 @@
+import { defineBuildConfig } from "unbuild";
+
+export default defineBuildConfig({
+	entries: ["./src/index"],
+	outDir: "dist",
+	declaration: true,
+	failOnWarn: false,
+	rollup: {
+		emitCJS: true,
+	},
+});
diff --git a/bun.lockb b/bun.lockb
new file mode 100755
index 0000000..47d072b
Binary files /dev/null and b/bun.lockb differ
diff --git a/package.json b/package.json
new file mode 100644
index 0000000..820dac7
--- /dev/null
+++ b/package.json
@@ -0,0 +1,29 @@
+{
+	"name": "bigint-quantile",
+	"type": "module",
+	"version": "0.0.1",
+	"exports": {
+		".": {
+			"import": "./dist/index.mjs",
+			"require": "./dist/index.cjs"
+		}
+	},
+	"main": "./dist/index.cjs",
+	"types": "./dist/index.d.ts",
+	"files": ["dist"],
+	"scripts": {
+		"build": "bunx unbuild",
+		"test": "bun test",
+		"test:coverage": "bun test --coverage",
+		"lint": "bunx biome check .",
+		"format": "bunx biome check . --write --unsafe"
+	},
+	"devDependencies": {
+		"@biomejs/biome": "1.9.1",
+		"@types/bun": "latest",
+		"unbuild": "^2.0.0"
+	},
+	"peerDependencies": {
+		"typescript": "^5.0.0"
+	}
+}
diff --git a/src/index.spec.ts b/src/index.spec.ts
new file mode 100644
index 0000000..96cd616
--- /dev/null
+++ b/src/index.spec.ts
@@ -0,0 +1,32 @@
+import { expect, it } from "bun:test";
+import { calculateQuantile } from "./";
+
+const data: bigint[] = [1n, 2n, 3n, 4n, 5n, 6n, 7n, 8n, 9n, 10n];
+
+it("should calculate 25th percentile / first quartile", () => {
+	const firstQuartile = calculateQuantile(data, 0.25);
+	expect(firstQuartile).toBe(3n);
+});
+
+it("should calculate 50th percentile / median", () => {
+	const median = calculateQuantile(data, 0.5);
+	expect(median).toBe(5n);
+});
+
+it("should calculate 75th percentile / third quartile", () => {
+	const thirdQuartile = calculateQuantile(data, 0.75);
+	expect(thirdQuartile).toBe(7n);
+});
+
+it("should throw error if quantile is not between 0 and 1", () => {
+	expect(() => calculateQuantile(data, 1.1)).toThrowError(
+		"Quantile must be between 0 and 1",
+	);
+	expect(() => calculateQuantile(data, -0.1)).toThrowError(
+		"Quantile must be between 0 and 1",
+	);
+});
+
+it("should return 0 if data is empty", () => {
+	expect(calculateQuantile([], 0.5)).toBe(0n);
+});
diff --git a/src/index.ts b/src/index.ts
new file mode 100644
index 0000000..8faeb21
--- /dev/null
+++ b/src/index.ts
@@ -0,0 +1,14 @@
+export const calculateQuantile = (data: bigint[], q: number): bigint => {
+	if (q < 0 || q > 1) throw new Error("Quantile must be between 0 and 1");
+	const sorted = data.sort((a, b) => (a < b ? -1 : a > b ? 1 : 0));
+	const pos = (sorted.length - 1) * q;
+	const base = BigInt(Math.floor(pos));
+	const rest = pos - Math.floor(pos);
+	if (sorted[Number(base)] === undefined) return 0n;
+	const result = sorted[Number(base)];
+	if (rest === 0) {
+		return result;
+	}
+	const next = sorted[Number(base) + 1] || sorted[Number(base)];
+	return result + ((next - result) * BigInt(Math.round(rest * 100))) / 100n;
+};
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 0000000..ffc08ab
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,27 @@
+{
+	"compilerOptions": {
+		// Enable latest features
+		"lib": ["ESNext", "DOM"],
+		"target": "ESNext",
+		"module": "ESNext",
+		"moduleDetection": "force",
+		"jsx": "react-jsx",
+		"allowJs": true,
+
+		// Bundler mode
+		"moduleResolution": "bundler",
+		"allowImportingTsExtensions": true,
+		"verbatimModuleSyntax": true,
+		"noEmit": true,
+
+		// Best practices
+		"strict": true,
+		"skipLibCheck": true,
+		"noFallthroughCasesInSwitch": true,
+
+		// Some stricter flags (disabled by default)
+		"noUnusedLocals": false,
+		"noUnusedParameters": false,
+		"noPropertyAccessFromIndexSignature": false
+	}
+}